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Old 3rd Apr 2017, 9:14 am   #21
Andrew2
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Default Re: Spectrum Analyser

Mr Bungle - if you are after reasonably-priced SMA patches, try SINEQUANON http://www.sinequanon.co.uk/amateur-...and-leads.html They have a very good selection at good prices. I think they are listed under 'amateur radio'.
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Old 3rd Apr 2017, 9:57 am   #22
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Default Re: Spectrum Analyser

Thanks for that link - those are quite reasonable. £4 for a semi-rigid and £2.50 for a short patch is within reasonable price range

I was looking at RS and Farnell before.

Edit:

Also have had to shelve my attempt for a couple of weeks to concentrate on dependencies. I got rid of my 225MHz counter a few days ago and have managed to get hold of two HP5328A counters which are only good to 120MHz as they are missing the C option. One of them is broken but has the DVM option so I can measure trigger voltage (sweep ramp) versus frequency so I can get real linearity data. The DVM module is broken however apparently so there's a repair job to do first. Hopefully one working counter will appear at the end.

Also this means I need to build a /10 prescaler that is good to a few hundred MHz. IC ordered for this and it'll go in a Pomona box I have lying around.

It's amazing how a simple thing escalates but that's what keeps life interesting

Last edited by MrBungle; 3rd Apr 2017 at 10:09 am.
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Old 3rd Apr 2017, 11:48 am   #23
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Default Re: Spectrum Analyser

Years ago I built up a complete set of parts for the G4PMK design. With all the PCBs connected together on a breadboard, I remember it working well but I never got round to assembling it in the ali case I had bought. The project was overtaken by the acquisition of a commercial SA. One of these days I will get round to posting it in the For Sale area!

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Old 10th May 2017, 7:57 pm   #24
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Default Re: Spectrum Analyser

I have now got a more complete analyser built to the G4PMK design, it is still a mess of wires and not properly set up yet but I am very pleased with the preliminary results. Pic 1 shows a 1MHz square wave, from my frequency counter, the span is set to 1MHz per division and narrow IF bandwidth (12.5kHz). Pic 2 shows the results with a short piece of wire connected to input, the MW broadcast stations are visible as are some signals around 5-6MHz. Pic 3 is the same as Pic 2 but with the If bandwidth set to wide (around 230kHz) I think the scan speed was a bit quick in Pic 2. Pic 4 shows the spectrum up to around 100MHz the large signal at around 20MHz is a spurious signal. I would be interested in seeing how Mr Bungle is getting on.

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Old 10th May 2017, 8:32 pm   #25
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Default Re: Spectrum Analyser

Quote:
Originally Posted by ParcGwyn View Post
I have now got a more complete analyser built to the G4PMK design, it is still a mess of wires and not properly set up yet but I am very pleased with the preliminary results.

Love it! Neat piece of kit, DAve!
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Old 10th May 2017, 9:18 pm   #26
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Default Re: Spectrum Analyser

Looks rather good to me

My attempts are shelved until July as I'm awaiting RS back ordered parts unfortunately. I ended up with two broken HP5328's in the end. Decided to wait and finish a couple of less ambitious projects to work on in the next month or two and get rid of some of the unneeded equipment I have. Also I ordered some SMA connectors from China which have yet to arrive.

I have built a comb generator however. I'll detail that when I know it works
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Old 21st May 2017, 7:13 pm   #27
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Default Re: Spectrum Analyser

I have decide to house the spectrum analyser in a case that includes a display, rather than use it as an oscilloscope adaptor. here are some pictures of the progress so far and some pictures of the rf attenuator. Before I dismantled it to place in the enclosure I attached a short wire antenna and switched on a toy walkie talkie. Two pictures show the noise generated by the super regen receiver and the transmitter signal. The walkie talkie is not CE marked and operates at around 27MHz.

Dave

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Old 21st May 2017, 7:15 pm   #28
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Final 2 pictures showing walie talkie in receive and transmit.

Dave

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Old 22nd May 2017, 3:48 pm   #29
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Default Re: Spectrum Analyser

Hi I reqularily use the G4PMK rad com simple spectrum analyser and initially got very hung up about setting the linearity of the sweep but when you take that as a feature and use the internal Xtal refs and when required an external signal generator to mark the peaks you have a very usable "simple " spactrum analyser.

Granted not up with the proffesional jobs but still very usable to check filters with a noise generator and spectrum purity of home brew transmitters. I also use it for plotting relative filter responses by manually stepping the frequency and reading the peaks.

It seems once you have one of these you invent tasks for it!!

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Old 22nd May 2017, 8:26 pm   #30
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Default Re: Spectrum Analyser

Yes, I have tried to get the frequency display linear but as you say it is not really necessary. Although I have not finished the analyser yet I have spent a lot of time playing with it. I am thinking of making simple tracking generator using a NE602 mixer from the VCO for filter alignment but a noise source may be simpler.

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Old 5th Jun 2017, 7:51 pm   #31
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Default Re: Spectrum Analyser

Spectrum analyser finally finished, with 3RP1A tube for use as a self contained instrument. Sockets have been included on the rear for connecting an oscilloscope and also audio out. I have spent a lot of time scanning the shortwave bands and using this as a shortwave receiver. I was quite surprised at the VCO stability.

Dave

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Old 5th Jun 2017, 8:33 pm   #32
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Default Re: Spectrum Analyser

Really nice work. Actually looks quite linear from the markers.

Edit: not much luck here. Awaiting a third counter to arrive and an RS back order that has been pushed back to July!
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Old 5th Jun 2017, 9:50 pm   #33
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Default Re: Spectrum Analyser

Well, it looks like you've got your membership card to that rather small group who have built their own scope or spectrum analyser!

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Old 5th Jun 2017, 9:51 pm   #34
ParcGwyn
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Default Re: Spectrum Analyser

Linearity is not too bad but the frequency response ends abruptly at 80MHz (VCO freq around 225MHz), haven't investigated yet but I think the VCO stops oscillating. Looking at the data sheet for a MC3356 the typical mixer oscillator operating range is 0.2-150MHz although the data sheet goes on to say that the oscillator has operated as high as 200MHz. So the device is being used outside the design parameters.

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Old 5th Jun 2017, 11:40 pm   #35
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Default Re: Spectrum Analyser

That's not a bad result really. I've tried pushing an NE602 up to its rated 200MHz and I hit a wall at merely 120MHz although I suspect that might be poor construction practice.
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Old 7th Jun 2017, 4:40 pm   #36
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Default Re: Spectrum Analyser

My new frequency counter arrived this morning and it had an OCXO in it which was a very nice surprise. It also had three leaked lead acid batteries but they came out easily and the whole thing cleaned up fine.

I have managed to bodge up a linear sweep generator this afternoon on a breadboard. I will make it more permanent when I build the VCO next.

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The above is generated with a 555 acting as a window comparator and trigger pulse generator. This watches and drains a BJT current source which is charging a high quality film capacitor. The current source controls the sweep rate. At the moment, there is a follower consisting of a 741. I will add any linearisation required and span/offset controls after this point, probably tomorrow!

Then on to the VCO.
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Old 7th Jun 2017, 5:30 pm   #37
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That looks nice and linear.
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Old 7th Jun 2017, 9:57 pm   #38
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Quote:
Originally Posted by MrBungle View Post
The above is generated with a 555 acting as a window comparator and trigger pulse generator. This watches and drains a BJT current source which is charging a high quality film capacitor. The current source controls the sweep rate.
Nice geometry!
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Old 7th Jun 2017, 10:28 pm   #39
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Default Re: Spectrum Analyser

Stuck at the PC for a bit so wrote up the sweep generator design info. This is constrained by the 555's divider arrangement to ramps between 1/3 and 2/3 VCC but there will be a summing amp and voltage amplifier to control the sweep mid-point and the range after the follower stage. C needs to be a decent quality unit, probably film based. I used a Vishay/BC MKT1813 as those things hold a good charge for days! Connect sweep trigger to the ext trigger on the scope and the output to the scope channel.

LF411 is better than 741. Use a CMOS 555 as they have much lower bias current. Any PNP can replace the 2n2907 but I like my metal can transistors
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Old 8th Jun 2017, 8:11 am   #40
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Nice diagram, what package did you use to create it?
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